This application claims priority under 35 U.S.C. §119(a) on Japanese Patent Application No. 2007-047567 filed in Japan on Feb. 27, 2007, the entire contents of which are herein incorporated by reference.
The present technology relates to a development apparatus that is applicable in an electrophotographic image forming apparatus such as a copier, printer, digital multifunction device, or the like, and to an image forming apparatus, and more specifically relates to a development apparatus and image forming apparatus in which an electrostatic latent image formed on an image bearing carrier is developed and made visible using a two-component developer having a toner and a carrier as main components.
In an electrophotographic image forming apparatus, the surface of an image bearing carrier (for example, a photosensitive body) is charged, an image is exposed in that charging area to form an electrostatic latent image, and the electrostatic latent image is developed and made visible with a development apparatus.
In a development apparatus that performs development using a two-component developer that includes a toner and a carrier, ordinarily a system is adopted in which a magnetic brush is formed in a developer bearing member, and only toner is affixed to the image bearing carrier. The development apparatus that performs development using a two-component developer, ordinarily, is provided with a developer tank in which the developer is stored, and a developer bearing member (for example, a developer roller) that bears the developer on the outer circumferential face and transports the developer to a developer area where the electrostatic latent image on the image bearing carrier is developed. In the developer bearing member, a plurality of magnets are disposed within a sleeve.
In this development apparatus, the carrier that has attracted the toner with a frictional charge is attracted in a brush-like shape to the outer circumferential face of the sleeve by the magnets inside the sleeve, thus forming a magnetic brush. The carrier attracted to the outer circumferential face of the sleeve is transported along with toner to the development area by rotating the sleeve relative to the magnets within the sleeve. A portion of toner that has been transported to the development area moves to the electrostatic latent image on the image bearing carrier due to a difference in electric potential between a development bias voltage applied to the sleeve and the electrostatic latent image, and thus the electrostatic latent image is developed to form a toner image. On the other hand, the carrier, in a state attracted to the outer circumferential face of the sleeve by the magnetic force of magnets inside the sleeve, is returned inside the developer tank along with toner that was not contributed to development.
Afterward, in the image forming apparatus, the toner image that has been formed on the image bearing carrier by development of the development apparatus is transferred to an intermediate transfer member such as an intermediate transfer belt or to a recording material such as recording paper. When the toner image has been transferred to an intermediate transfer member, the toner image is further transferred to a recording material, and then fixed to the recording material by a fixing apparatus.
In this sort of image forming apparatus, during development, carrier may scatter from the magnetic brush in the developer bearing member and become affixed to the image bearing carrier. Carrier that is affixed to the image bearing carrier will reduce adhesion of the intermediate transfer member or the recording material to the image bearing carrier during transfer, causing white or omitted characters when performing transfer to the intermediate transfer member or the recording material. Also, carrier may scatter from the magnetic brush in the developer bearing member and fall to the inside of the image forming apparatus. This will cause a malfunction or the like of the image forming apparatus.
In particular, the diameter of the carrier used in the developer has become smaller as image quality of image forming apparatuses has increased in recent years, and the developer transport speed (for example, rotational speed of a developer roller) of the sleeve in the developer bearing member has increased as the speed of image forming processing has increased. As a result, there is a tendency for the affixing force of the sleeve and the carrier to weaken, and thus the above problems have become pronounced.
Therefore, in development apparatuses often a carrier recovery member is provided near the downstream side in the developer transport direction of the developer bearing member from the development area.
In a development apparatus provided with this carrier recovery member, ordinarily, a plurality of magnets are provided inside a carrier recovery roller. The carrier recovery roller is rotated relative to the inside magnets when development is performed. Carrier that affixes to the image bearing carrier during development is attracted to the outer circumferential face of the carrier recovery roller by the magnetic force of the magnets inside the rotated carrier recovery roller. Carrier that has been attracted to the outer circumferential face of the carrier recovery roller is scraped from the outer circumferential face by a scraper disposed in contact with the outer circumferential face, recovered within the developer tank, and reused.
In this development apparatus, a configuration is adopted in which, among the magnetic poles within the carrier recovery roller, a magnetic pole for attracting the carrier from the image bearing carrier is positioned so as to face the surface of the image bearing carrier (see JP H9-34263A, lines 7-9 of paragraph [0010] and FIG. 3, and JP H7-98545A, lines 5-6 of paragraph [0027] and FIG. 2).
More specifically, in such a conventional development apparatus, it is assumed that carrier that, during development, scattered in the magnetic brush in the developer bearing member, moved to the image bearing carrier, and then affixed on the image bearing carrier is recovered. Because a magnetic pole for attracting carrier is positioned so as to face the surface of the image bearing carrier, there is no consideration of carrier that scatters in the magnetic brush, or example, carrier that scatters in the magnetic brush and is at a stage of moving to the image bearing carrier, or carrier that scatters in the magnetic brush and attempts to drop inside the image forming apparatus.
Also, in the conventional development apparatus, a plurality of magnetic poles are provided within the carrier recovery roller, including a magnetic pole for attracting carrier, so the surface area of each magnetic pole face is reduced. Such a configuration has the disadvantage that the strength of the magnetic poles is not large, so in reality it is not possible to effectively recover carrier when performing development, and this leads to a deterioration in print quality.
The present technology was made in view of the above problems, and it is an object thereof to provide a developer apparatus and image forming apparatus in which a carrier that is scattered in a magnetic brush in a developer bearing member during development can be recovered into a developer tank, and thus it is possible to eliminate problems due to carrier scattering such as a deterioration in image quality.